ISSN 1067-4136, Russian Journal of Ecology, 2007, Vol. 38, No. 3, pp. 204–211. © Pleiades Publishing, Ltd., 2007. Original Russian Text © Yu.V. Bespalaya, I.N. Bolotov, A.A. Makhrov, 2007, published in Ekologiya, 2007, Vol. 38, No. 3, pp. 222–229. State of the Population of the European Pearl Mussel Margaritifera margaritifera (L.) (Mollusca, Margaritiferidae) at the Northeastern Boundary of Its Range (Solza River, White Sea Basin) Yu. V. Bespalayaa, I. N. Bolotova, and A. A. Makhrovb a Institute of Ecological Problems of the North, Ural Division, Russian Academy of Sciences, nab. Severnoi Dviny 23, Arkhangelsk, 163000 Russia; e-mail:
[email protected] b Vavilov Institute of General Genetics, Russian Academy of Sciences, ul. Gubkina 3, Moscow, 119991 Russia Received March 9, 2006 Abstract—Only two river basins in which the European pearl mussel has survived to date are known in Arkhangelsk oblast. These are the Solza and Kozha basins. The northeastern boundary of the European range of this species passes along the watershed between the basins of the Solza and the Shirshema (the Onega Pen- insula) and then along the Onega–Northern Dvina watershed. The population density and the proportion of juveniles widely vary in different parts of the Solza Basin, and, therefore, the previously conclusion concerning the ageing of the population in the Kazanka River (Bolotov and Semushin, 2003) applies only to certain parts of this river. The highest density of the pearl mussel in the Solza Basin is 68 ind./m2. Fish cultivation contributes to the conservation of this pearl mussel population, as the release of Atlantic salmon juveniles ensures repro- duction of the mollusk under conditions of regulated river flow.